1. Field of the Invention
This invention pertains to the field of bioaffecting compositions; more specifically, it pertains to insecticidal compositions containing organic active ingredients comprising N'-aryl-N-methylformamidines and 3-phenoxybenzyl carboxylates and to the use of the compositions for controlling insects.
2. Description of the Prior Art
3-Phenoxybenzyl carboxylate insecticides, such as 3-phenoxybenzyl 3-(2,2-dihalovinyl)-2,2-dimethylcyclopropanecarboxylates, are of great interest currently because, unlike previous compounds of this type, such as the natural pyrethrins, they have good photo-oxidative stability. Pyrethrins have long been of interest because they are active against a wide range of insect species, they display relatively low toxicity toward mammals, and they do not leave harmful residues. However, pyrethrins and the newer 3-phenoxybenzyl carboxylates are very costly, and ways to increase their cost effectiveness are actively being sought.
Synergists are used commercially in combination with pyrethrins because they lessen the amount of insecticide required and thus reduce the cost at which insect control is achieved. Some of the most widely used synergists for pyrethrins are methylenedioxyphenyl compounds; piperonyl butoxide is a well-known example [U.S. Pat. No. 2,550,737]. More recently, mono(alkyl and alkenyl) mono-.omega.-alkynyl arylphosphonates were recognized as synergists [U.S. Pat. Nos. 3,885,031 and 3,944,666]. The latter also synergize the insecticidal activity of 3-phenoxybenzyl 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate.
Control of insects of the order Lepidoptera, genus Heliothis, is important to the successful growth of cotton and other important crops. The tobacco budworm, Heliothis virescens, is a major late season pest of cotton. This insect is resistant to most insecticides now registered for use against it. The bollworm, Heliothis zea, is also a major cotton pest. Attempts to synergize insecticides against Heliothis have not been very successful. It is known, however, that the activity of pyrethrins and the synthetic pyrethroid, tetramethrin, against Heliothis can be increased by admixture of N'-(4-chloro-2-methylphenyl)-N,N-dimethylformamidine, chlorodimeform [Plapp, J. Econ. Entomol., 69, 91 (1976)], but neither pyrethrins nor tetramethrin are 3-phenoxybenzyl carboxylates.
Bacillus thuringiensis in combination with chlordimeform also exhibits synergism [Creighton, et al., J. Econ. Entomol., 67, 102 (1974)]. Chlordimeform is an acaricide and an ovicide but has limited insecticidal activity. [Knowles, et al., J. Econ. Entomol., 66, 1245 (1973); Wolfenbager, et al., ibid., 67, 445 (1973)].